Elevator installations comprise an elevator car and elevator doors, particularly a car door and shaft doors. For example, a shaft door is provided with at least one door contact switch by means of which it is monitored whether the shaft door is unlocked. Such door contact switches arranged at each individual shaft door are incorporated in a safety circuit. If one of these shaft doors is unlocked, the safety circuit is interrupted. In that way the elevator car can be moved only when all shaft doors of the elevator installation are locked. Moreover, further settings of such an elevator door can be monitored by means of door contact switches, particularly an open setting or closed setting.
WO 2006036146 shows a switching device for monitoring a door leaf belonging to an elevator door. The elevator door comprises, apart from the door leaf, a door surround, wherein the door leaf is lockable to the door surround. The switching device comprises a plurality of magnets and an equal number of proximity sensors. The magnets are arranged at the door leaf and the proximity sensors fastened to the door surround. Each of these proximity sensors is associated with exactly one individual magnet. In that case, the magnets have a defined geometric arrangement relative to one another. This defined geometric arrangement is equally imaged by the proximity sensors in such a way that the magnets simultaneously activate the proximity sensors on transition of the door leaf to its locked setting. This means that each proximity sensor has the same spacing from the magnet associated therewith. By means of a switching device defined in such a way it is possible to avoid simulation by an unauthorized person, by way of a permanent magnet held at the proximity sensors, a locked setting of the relevant elevator door even though this elevator door is, for example, still open.
It is problematic with such a switching device that such a spacing, which triggers the unlocked setting, of the magnets from the proximity sensors associated therewith can equally be influenced by faulty settings of, for example, a damaged door leaf. This means that a deviation of the magnets from their intended movement path near the locked setting of the door leaf signifies a displacement of the locked setting itself, which in turn can lead to failure of the elevator door and consequently to shutdown of the elevator installation.